1. Field of the Invention
The present invention relates to an interface circuit, and more particularly to a logic interface circuit for shifting levels of supply voltages and a semiconductor memory device to which the logic interface circuit is applied, where the logic interface circuit uses logic gates such as inverter, a NAND gate, and a NOR gate.
2. Description of the Prior Art
In general, a level shifter is used for changing and outputting levels of input signals. That is, the level shifter is a circuit to change a CMOS level of a signal into a TTL level of a signal and output it, or vice versa
In case that two functional blocks inside a chip has different supply voltages, the level shifter as such can be used to interface between the two blocks. However, general level shifters are made with complicated structures, which increases the space required for the chip.
For example, a semiconductor memory device is constructed with a plurality of functional blocks. In order to improve the operational speed of the semiconductor memory device by making the levels of supply voltage different among the functional blocks, a level shifter should be additionally provided between those different functional blocks. In other words, if at least more than two supply voltages are applied to the semiconductor device, a level shifter should be added to interface between those functional blocks which have different supply voltages.
However, if the level shifter as such is added to the chip, the circuit of the semiconductor memory device becomes complicated, thereby increasing the area for the chip.